1. Field of the Invention
The present invention relates to a device used for boring a subterranean wellbore. More specifically, the invention relates to a rotary drag bit having blades with recesses and nozzles in the recesses.
2. Description of the Related Art
Drill bits used for creating subterranean wellbores typically comprise one of a rotary tri-cone drill bit or a drag bit. Drag bits are typically comprised of a single body molded from a combination of tungsten carbide with a steel core. The body includes raised portions referred to as blades that mm along the face of the bit body. The blades have recesses formed thereon extending generally perpendicular to the blade. The inserts or cutters are anchored within the recesses generally by welding, braising, or some other fastening means. Additionally, fluid nozzles are generally provided along the bit base for injecting fluid while drilling to wash away cuttings formed during the drilling process, as well as for cooling the drill bit.
Drill bits are typically connected to the end of a drill string where the upper end of the drill string is coupled with a drive means for rotating the string, thus, rotatingly operating the drill bit during drilling operations. The drill bit cuts through the subterranean formation by fracturing and/or shearing the rock formation. The drilling fluid or mud is pumped through the drill string down through the bit to perform the previously mentioned cleaning and cooling functions. Additionally, the inserts may include a polycrystalline diamond compact (PDC) on the bit face. Thus, drag bits having a PDC insert are referred to as PDC bits. PDC bits are generally employed in formations classified as having a soft to medium hardness. Several parameters determine drill bit performance, such as mud type, revolutions per minute, weight on bit, drill string, and the formation. The performance of the bit is evaluated as a rate of penetration.
One characteristic of a PDC drill bit is its stability, which reduces the magnitude of vibration at the bottom hole assembly. When the rotational axis is offset of the geometrical center of the bit, a “whirling” effect is produced which overloads the amount of cuttings in the wellbore. The PDC blade shape, hydraulics, and density/size of the cutters affect bit performance. Standard PDC bits are characterized by an inclusion of several blades, each consisting of a solid piece of material extending from the bit face. These bits can sometimes experience a phenomenon referred to as “balling”, which refers to the collection of soft formation on the bit face. The soft formation collected on the bit face reduces the cutting contact therefore decreasing bit performance. The “balling” requires cleaning of the bit which may consume a considerable time of rig time for pumping and/or a bit trip.